Major Depressive Disorder (MDD) is one of the most prevalent mental disorders, and is associated with significant mortality, morbidity, and economic costs. The Stony Brook Temperament Study is an ongoing longitudinal study that seeks to identify early behavioral precursors/risk factors for depression and understand the neurobiological and psychosocial processes through which these early manifestations develop into MDD. This information about risk pathways and processes should contribute to understanding when and how to intervene in order to prevent the disorder and limit its progression. The study initially assessed a large community sample of 3-year old children, followed them up at age 6, and is currently evaluating them in middle childhood (age 9). This competing renewal application seeks to extend the study into adolescence, the beginning of the peak risk period for onset of MDD. Specifically, the application proposes to map pathways from laboratory observations of low positive emotionality and high negative emotionality at age 3 to neural indices of emotional and social information processing, hypothalamic-pituitary-adrenal axis dysregulation, and emerging depressive and anxiety symptoms in early- (age 12) and mid- (age 15) adolescence. In addition, it seeks to understand the role of pubertal development and life stress in influencing these trajectories, and to capture the early portion of the expected sure in first-onset MDD that begins at puberty and continues through early adulthood.